Bitumens are often used as a binder material in asphalts used to pave roads or other surfaces. Examples of bitumens that may be used in the compositions and methods of the present invention include natural bitumens, pyrobitumens and artificial bitumens. Bitumens that are particularly preferred are those used for roadways, such as asphalt or maltha. Asphalt paving material is made by mixing the asphalt binder with aggregate.
Asphalt binders comprising bitumens are frequently used in applications where there can be a wide variation in environmental conditions, particularly when used in pavements. Accordingly, the properties of the asphalt binder in high and low temperature conditions is a concern. At low temperatures, some binder materials can become brittle, leading to long transverse fissures due to thermal stress. At higher temperatures, the asphalt binder becomes more fluid (i.e. the viscosity is lower), which can lead to rutting of a pavement due to the passage of vehicles over the surface. Resistance to fatigue and impact, and the adherence of the asphalt binder to aggregate in paving applications, are properties of a particular binder that also must be considered in particular applications. Some asphalt binders may require a relatively high elastic behavior, for example where the corresponding asphalt paving mixture is used in areas of high traffic rates and high loads.
Various methods have been developed in an attempt to improve the plasticity of bitumens and improve the wear of asphalts made using the bitumen binders. For example, in U.S. Pat. No. 5,618,862, a method is described in which bitumen is combined with a sulfur-crosslinkable elastomer and a sulfur donating coupling agent to form a sulfur vulcanized reaction mixture. The sulfur vulcanized reaction mixture is then combined with an acid adjuvant to produce a modified bitumen product. According to this method, the acid adjuvant is not added to the bitumen until after the sulfur vulcanization is complete.
It would be desirable for having a method for making a modified bitumen for use in asphalts that is simplified. Accordingly, among the objects of the present invention is to provide methods of making a modified bitumen material with improved elasticity, and having acceptable properties for use as a binder material in asphalt pavements.